Oled devices with internal outcoupling

ABSTRACT

Optoelectronic devices with enhanced internal outcoupling include a substrate, an anode, a cathode, an electroluminescent layer, and an electron transporting layer comprising inorganic nanoparticles dispersed in an organic matrix.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional of and claims priority from U.S.provisional application Ser. No. 61/694,427, filed 29 Aug. 2012, theentire disclosure of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under contract numberDOE DE-EE0003250 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

BACKGROUND

Organic light-emitting devices (OLEDs) have shown great potential forgeneral illumination. A typical OLED consists of one or more organiclayers sandwiched between two electrodes, which are stacked on asupporting substrate such as glass and plastic sheet. The OLED operatesas an electroluminescent device. Light generated in the organic layerspropagates in all the directions.

State-of-the-art OLED emissive materials generally have a refractiveindex greater than 1.7 that is substantially higher than that of most ofthe supporting substrates (usually ˜1.5). As light propagates from ahigher index medium to a lower index medium, total internal reflection(TIR) occurs for light beams travelling in large oblique angles relativeto the interface, according to Snell's law. TIR leads to power trappingin the higher index medium and reduces light extraction efficiency. In atypical OLED device, TIR occurs between organic layers (refractive index˜1.7) and the substrate (refractive index ˜1.5); and between thesubstrate (refractive index ˜1.5) and air (refractive index 1.0), whichleads to light trapping in the “organic modes” as well as the “substratemodes”. In addition, some of the emitted light is coupled to “surfaceplasmon mode”, which is a surface wave traveling along the metalcathode-ETL interface. This results in light trapping in the device andfurther reduces light extraction efficiency. Thus, an OLED, in itssimplest form, usually exhibits poor light extraction efficiency. It iscommonly believed that only ˜20% of light generated can escape from anOLED device without any light extraction mechanism.

Different technical methods and approaches have been used to improvelight extraction. Examples include substrate surface roughening, surfacetexturing, such as 2D photonic structures, the use of microlenses, andthe use of scattering films. These approaches have led to enhancementsin light extraction through substrate modification and optimization.However, work in the field to date has mainly focused on substratemodification.

In dry-coated OLEDs, all the organic layers have similar refractiveindex. For wet-coated OLEDs, however, state-of-the-art OLEDs typicallyemploy a p-doped polymeric hole-injection layer (HIL); a well-knownexample of a polymeric HIL is PEDOT:PSS. Most of the p-doped polymericHILs have a refractive index of <1.5, which is much less than that ofstate-of-the-art OLED emissive materials (typically >1.7). As a result,additional TIR occurs at the EML-HIL interface and further reduces lightextraction efficiency. For planarization of the anode, typical thicknessof HIL is greater than 100 nm. However, as the thickness of HILincreases, light penetration through HIL decays further. For example, ina low index HIL, EQE decreases with increasing HIL thickness because ofthe TIR at the emissive layer and HIL interface, resulting in anadditional 14% loss in emitted power. Therefore, the mismatch inrefractive index is one of the limiting factors for light extractionefficiency in wet-coated OLEDs, and there is a need to improve lightextraction from wet-coated OLED devices.

BRIEF DESCRIPTION

Light extraction from wet-coated OLED devices may be improved byoptimizing the charge injection or transport layers to direct more lightinto a supporting substrate, thus maximizing the final light extractionefficiency. Accordingly, in one aspect, the present invention relates toan optoelectronic device that has at least one charge carrier injectingor transporting layer that includes inorganic nanoparticles having abimodal particle size distribution and dispersed in an organic matrix.In another aspect, the present invention relates to an optoelectronicdevice that includes an electron transporting layer comprising inorganicnanoparticles dispersed in an organic matrix. In yet another aspect, thepresent invention relates to an optoelectronic device wherein thesurface of the electron transporting layer that is contiguous to thecathode is uneven.

In yet another aspect, the present invention relates to anoptoelectronic device comprising

a substrate;

an anode;

a cathode;

an electroluminescent layer; and

electron transporting layer comprising a fluoro compound of formula I

(Ar²)_(n)—Ar¹—(Ar²)_(n)  I

whereinAr¹ is C₅-C₄₀ aryl, C₅-C₄₀ substituted aryl, C₅-C₄₀ heteroaryl, orC₅-C₄₀ substituted heteroaryl;Ar² is, independently at each occurrence, fluoro- orfluoroalkyl-substituted C₅₋₄₀ heteroaryl; andn is 1, 2, or 3.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a cross sectional view of an optoelectronic device having ahole injecting layer that contains a population of inorganicnanoparticles having a bimodal particle size distribution.

FIG. 2 is a cross sectional view of an optoelectronic device having anelectron transporting layer that contains inorganic nanoparticles.

FIG. 3 is a cross sectional view of an optoelectronic device having apatterned electron transporting layer.

FIG. 4 is a cross sectional view of an optoelectronic device havingpatterned layers.

DETAILED DESCRIPTION

FIG. 1 illustrates a first embodiment of an optoelectronic deviceaccording to the present invention. Device 10 includes substrate 1,anode 2, hole injecting layer 3, hole transporting layer 4,electroluminescent layer 5; electron transporting layer 6, and cathode7. Electron transporting layer 6 contains a population of inorganicnanoparticles 11. Mean particle size of the inorganic nanoparticles 11ranges from about 10 nm to about 100 nm, particularly from about 30 nmto about 100 nm. Average distance between adjacent particles may rangefrom about 250 nm to about 600 nm, and distribution of the particles maybe pseudo-periodic.

Refractive index of the inorganic nanoparticles 11 is at least 0.1 lessthan that of the organic material or organic matrix of electrontransporting layer 6, particularly at least 0.2 less than that of theorganic matrix. Suitable materials for the organic matrix of electrontransporting layer 6 include compounds containing a pyridinyl group,that is, compounds containing a pyridine ring, particularly thosecontaining a phenyl pyridinyl group. Examples of suitable materials forelectron transporting layer 6 are described in but are not limited to,poly(9,9-mono- or disubstituted fluorene), tris(8-hydroxyquinolato)aluminum (Alq3), 2,9 dimethyl-4,7-diphenyl-1,1-phenanthroline,4,7-diphenyl-1,10-phenanthroline,2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole,3-(4-biphenylyl)-4-phenyl-5 (4 t butylphenyl)-1,2,4-triazole,1,3,4-oxadiazole-containing polymers, 1,3,4-triazole-containingpolymers, quinoxaline-containing polymers, cyano-PPV, and particularly,compounds containing phenyl pyridine units, as described in U.S. Pat.No. 8,062,768 and U.S. Pat. No. 8,039,125. Refractive index of suitablematerials is typically about 1.7. Where these materials are used as theorganic matrix of electron transporting layer 6, refractive index ofinorganic nanoparticles 11 less than 1.7, particularly less than about1.5, more particularly less than about 1.4.

Inorganic nanoparticles 11 are composed of a metal oxide or alkali metalfluoride or alkali earth metal fluoride dielectric material,particularly a metal oxide. Suitable metal oxides include indium tinoxide, titanium oxide, zinc oxide zirconium oxide, hafnium oxide,rhodium oxide, tungsten oxide, molybdenum oxide, vanadium oxide, siliconoxide, and combinations thereof. Suitable alkali metal fluorides includeLiF, NaF, KF, RbF and combinations thereof; suitable alkali earth metalfluorides include BeF₂, MgF₂, CaF₂, SrF₂, BaF₂ and combinations thereof.In particular, LiF, NaF, CaF₂ and combinations thereof may be used.Inorganic nanoparticles 11 may be spherical or elliptical, but physicalform or shape is not limited, and other forms, for example, flatplatelets, may be used. The nanoparticle may be solid or have acore-shell structure. Concentration of the inorganic nanoparticles inelectron transporting layer 6 ranges from about 5% by weight to about50% by weight, particularly from about 10% by weight to about 30% byweight, more particularly from about 15% by weight to about 25% byweight.

FIG. 1 shows the inorganic nanoparticles located at the surface ofelectron transporting layer 6 adjacent to cathode 7, that is, at theETL/cathode interface, or, where an electron injecting layer is includedin the device between the electron transporting layer and the electroninjecting layer, at the ETL/EIL cathode interface. In other embodiments,the inorganic nanoparticles may be located in one or more of the otherlayers of the device, in addition to electron transporting layer 6,including hole injecting layer 3, hole transporting layer 4, andelectroluminescent layer 5.

Substrate 1 is typically composed of glass or a transparent plastic, andmay include a barrier layer. Materials suitable for use in anode 2include, but are not limited to, materials having a bulk resistivity ofless than about 1000 ohms per square, as measured by a four-point probetechnique. A solid layer of a transparent conductive oxide (TCO) may beused, or a discontinuous matrix of metallic rods, such as a mesh or gridcomposed of metallic nanowires, or a film composed of metal,particularly silver, nanowires, may be used. Indium tin oxide (ITO) isfrequently used as the anode because it is substantially transparent tolight transmission and thus facilitates the escape of light emitted fromelectro-active organic layer. Other oxides that may be utilized as theanode layer include tin oxide, indium oxide, zinc oxide, indium zincoxide, zinc indium tin oxide, antimony oxide, and mixtures thereof. Thenanowires may be used with the TCO layer, or may be used alone, allowingdirect contact between substrate 1 and hole injecting layer 3.

Materials suitable for use in hole injecting layer 3 include3,4-ethylenedioxythiophene (PEDOT) and blends of PEDOT with polystyrenesulfonate (PSS), commercially available from H.C. Stark, Inc. under theBAYTRON® trade name. Materials suitable for use in hole transportinglayer 4 include, but are not limited to, PEDOT, PEDOT:PSS,1,1-bis((di-4-tolylamino) phenyl)cyclohexane,N,N′-bis(4-methylphenyl)-N,N′-bis(4-ethylphenyl)-(1,1′-(3,3′-dimethyl)biphenyl)-4,4′-diamine,tetrakis-(3-methyl-phenyl)-N,N,N′,N′-2,5-phenylenediamine,phenyl-4-N,N-diphenylaminostyrene, p-(diethylamino) benzaldehydediphenylhydrazone, triphenylamine,1-phenyl-3-(p-(di-ethylamino)styryl)-5-(p-(diethylamino)phenyl)pyrazoline, 1,2-trans-bis(9H-carbazol-9 yl)cyclobutane,N,N,N′,N′-tetrakis-(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, copperphthalocyanine, polyvinylcarbazole, (phenylmethyl)polysilane,polyaniline, polyvinylcarbazole, triaryldiamine, tetraphenyldiamine,aromatic tertiary amines, hydrazone derivatives, carbazole derivatives,triazole derivatives, imidazole derivatives, oxadiazole derivativeshaving an amino group, and polythiophenes as disclosed in U.S. Pat. No.6,023,371.

Materials suitable for use in electroluminescent layer 5 include, butare not limited to, electroluminescent polymers such as polyfluorenes,preferably poly(9,9-dioctyl fluorene) and copolymers thereof, such aspoly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)diphenylamine)(F8-TFB); poly(vinylcarbazole) and polyphenylene-vinylene and theirderivatives. In addition, the light emitting layer may include a blue,yellow, orange, green or red phosphorescent dye or metal complex, or acombination thereof. Materials suitable for use as the phosphorescentdye include, but are not limited to, tris(1-phenylisoquinoline) iridium(III) (red dye), tris(2-phenylpyridine) iridium (green dye) and Iridium(III) bis(2-(4,6-difluorephenyl)-pyridinato-N,C2) (blue dye).Commercially available electrofluorescent and electrophosphorescentmetal complexes from ADS (American Dyes Source, Inc.) may also be used.ADS green dyes include ADS060GE, ADS061GE, ADS063GE, and ADS066GE,ADS078GE, and ADS090GE. ADS blue dyes include ADS064BE, ADS065BE, andADS070BE. ADS red dyes include ADS067RE, ADS068RE, ADS069RE, ADS075RE,ADS076RE, ADS067RE, and ADS077RE.

Materials suitable for use as cathode 7 include general electricalconductors including, but not limited to, metals and metal oxides suchas ITO which can inject negative charge carriers (electrons) into theinner layer(s) of the OLED. Metals suitable for use as the cathodeinclude K, Li, Na, Cs, Mg, Ca, Sr, Ba, Al, Ag, Au, In, Sn, Zn, Zr, Sc,Y, elements of the lanthanide series, alloys thereof, and mixturesthereof. Suitable alloy materials for use as the cathode layer includeAg—Mg, Al—Li, In—Mg, Al—Ca, and Al—Au alloys. Layered non-alloystructures may also be employed in the cathode, such as a thin layer ofa metal such as calcium, or an alkali metal fluoride or alkali earthmetal fluoride, such as LiF, covered by a thicker layer of a metal, suchas aluminum or silver. In particular, the cathode may be composed of asingle metal, and especially of aluminum or silver metal.

FIG. 2 illustrates a second embodiment of an optoelectronic deviceaccording to the present invention. Device 20 includes substrate 1,anode 2, hole injecting layer 3, hole transporting layer 4,electroluminescent layer 5; electron transporting layer 6, and cathode7. Hole injecting layer 3 contains a population of inorganicnanoparticles having a bimodal particle size distribution, and includesinorganic nanoparticles 11 of a first subpopulation and inorganicnanoparticles 12 of a second subpopulation. Mean particle size ofinorganic nanoparticles 11 ranges from about 10 to about 100 nm, and ofinorganic nanoparticles 12 ranges from about 50 nm to about 10000 nm,particularly 5000 nm. Average distance between adjacent particles mayrange from about 250 nm to about 600 nm, and distribution of theparticles may be pseudo-periodic.

Refractive index of the inorganic nanoparticles 11 and 12 is at least0.1 greater than that of the organic material or organic matrix of thelayer, particularly at least 0.2 greater than that of the organicmatrix. Suitable materials for the organic matrix of hole injectinglayer 3 include polymers derived from a thiophene monomer, such asPEDOT, which has typically has a refractive index of about 1.5. WherePEDOT is used as the organic matrix of hole injecting layer 3,refractive index of inorganic nanoparticles 11 and 12 is at least 1.6,particularly at least 1.7, more particularly at least 2.0. Inorganicnanoparticles 11 and 12 may have the same refractive index, or therefractive index of the two subpopulations may be different.

Inorganic nanoparticles 11 and 12 are composed of a metal oxide, alkalimetal fluoride, or alkali earth metal fluoride dielectric material,particularly a metal oxide. Suitable alkali metal fluorides include LiF,NaF, KF, RbF and combinations thereof; suitable alkali earth metalfluorides include BeF₂, MgF₂, CaF₂, SrF₂, BaF₂ and combinations thereof.In particular, LiF, NaF, CaF₂ and combinations thereof may be used.Suitable metal oxides include silicon oxide, titanium oxide, zirconiumoxide, zinc oxide, and combinations thereof. Subpopulation 11 andsubpopulation 12 may be composed of the same material, or may havedifferent compositions. Inorganic nanoparticles 11 and 12 may bespherical or elliptical, but physical form or shape is not limited, andother forms, for example, flat platelets, may be used. The nanoparticlemay be solid or have a core-shell structure. Concentration of theinorganic nanoparticles in hole injecting layer 3 ranges from about 5%by weight to about 50% by weight, particularly from about 10% by weightto about 30% by weight, more particularly from about 15% by weight toabout 25% by weight.

FIG. 2 shows the inorganic nanoparticles located in the interior of holeinjecting layer 3. In other embodiments, the inorganic nanoparticles maybe located at the surface of hole injecting layer 3 adjacent to holetransporting layer 4, that is, at the HIL/HTL interface. In yet otherembodiments, the inorganic nanoparticles may be located in one or moreof the other layers of the device, in addition to hole injecting layer3, including hole transporting layer 4, electroluminescent layer 5; andelectron transporting layer 6.

FIG. 3 illustrates a third embodiment of an optoelectronic deviceaccording to the present invention. Device 30 includes substrate 1,anode 2, hole injecting layer 3, hole transporting layer 4,electroluminescent layer 5; electron transporting layer 6, and cathode7, wherein a surface of the electron transporting layer contiguous tothe cathode, at the ETL/cathode interface, is uneven due to patterningof electron transporting layer 6. It should be noted that FIG. 1 alsoshows an embodiment wherein the surface of electron transporting layer 6is uneven. In FIG. 1, inorganic nanoparticles are disposed at theinterface, causing the surface and interface to be uneven or non-planar.The uneven surface may be formed by patterning electron transportinglayer 6 using photolithography, nanolithography, nanoimprintlithography, including photo nanoimprint lithography, soft lithography,or surface roughening through phase-separation, polymer demixing, orcolloidal lithography. Alternatively, the uneven surface may be formedby patterning of the underlying layers. FIG. 4 illustrates an embodimentwherein surfaces of hole injecting layer 3, hole transporting layer 4,electroluminescent layer 5; and electron transporting layer 6 arepatterned. Methods of forming the patterned layers are not limited; allpatterned layers may be formed by the same method, or different layersmay be formed by different methods, or patterning of an underlying layermay result in the pattern being formed in the overlying layer.

Distribution of the elements of the pattern(s) may be pseudo-periodic.The pattern may be one-dimensional or two-dimensional, and period of thepattern may range from about 250 nm to about 600 nm. Pattern geometry isnot limited, and many different shapes may be used.

In other embodiments, optoelectronic devices according to the presentinvention include an electron transporting layer comprising a fluorocompound of formula I; refractive index of such materials typicallydecreases with higher fluorine content

(Ar²)_(n)—Ar¹—(Ar²)_(n)  I

wherein

-   -   Ar¹ is C₅-C₄₀ aryl, C₅-C₄₀ substituted aryl, C₅-C₄₀ heteroaryl,        or C₅-C₄₀ substituted heteroaryl;    -   Ar² is, independently at each occurrence, fluoro- or        fluoroalkyl-substituted C₅₋₄₀ heteroaryl; and    -   n is 1, 2, or 3.

In particular embodiments, Ar¹ is C₅-C₄₀ heteroaryl; more particularly,Ar¹ is

and Ar³ is a direct bond, C₅-C₃₅ aryl, or C₅-C₃₅ heteroaryl. In otherparticular embodiments, Ar² is

Ar₄ is a direct bond, C₅-C₃₅ aryl, or C₅-C₃₅ heteroaryl and R is fluoroor fluoroalkyl.

Suitable aryl or heteroaryl groups from which Ar¹ may be selectedinclude phenyl, pyridinyl, carbazolinyl, furanyl, carbolinyl, fluorenyl,thiophenyl, and biphenyl. Suitable fluoro- or fluoroalkyl-substitutedaryl or heteroaryl groups from which Ar² may be selected includepyridinyl, carbazolinyl, furanyl, carbolinyl, fluorenyl, thiophenyl, andbiphenyl, each being fluoro- or fluoroalkyl-substituted, that is,containing at least one fluoro, or fluoroalkyl, substituent.

Fluoro compounds for use in optoelectronic device according to thepresent invention include

In yet another aspect, the present invention relates to fluoro compoundsof formula II, and devices containing them,

wherein

-   -   Ar³ is independently at each occurrence a direct bond, C₅-C₃₅        aryl, or C₅-C₃₅ heteroaryl.        In particular embodiments, Ar³ is independently at each        occurrence phenyl, pyridinyl, or biphenyl.

In yet another aspect, the present invention relates to anoptoelectronic device that includes a substrate, an anode, a cathode, anelectroluminescent layer; and an electron transporting layer comprisinga fluorine-substituted compound.

EXAMPLES Example 1 Preparation of 6-CF3 ETL Compound (5)

A 6-CF3 ETL compound (5) was prepared according to the general procedureshown in Scheme 1.

Boronic acid 2 shown in Scheme 1 was prepared according to a literatureprocedure (Org. Biomol. Chem. 2009, 7, 2155-2161). A flame dried flaskwas charge with triisopropyl borate (6.2 mL, 26.5 mmol),3-bromo-5-trifluormethyl pyridine (5.0 g, 22.1 mmol), and THF (40 mL)under an inert atmosphere of nitrogen and was then subsequently cooledto −78° C. To this solution was added butyl lithium (10 mL, 24.6 mmol,2.5 M in Hexanes) under controlled conditions. The reaction mixture wasstirred at −78° C. for 3.5 h and was then allowed to warm to −10° C. Atthis temperature water was added (40 mL) and the contents of the flaskwere transferred to a single neck flask and the volatile solvents wereremoved. The water solution was treated with 3 pellets of NaOH and afterthey dissolved the water layer was washed with Et₂O. The pH of the waterwas adjusted to 5.0 by adding AcOH. The heterogenous mixture wastransferred to a separatory funnel and the H₂O layer was extracted withEtOAc. The solvents were evaporated to dryness to give an off-whitesolid. ¹H NMR compound 2.HOAc (400 MHz, DMSO+HCl_((aq)), 25° C.) δ 1.89(s, 3H), 8.75 (s, 1H), 9.12 (d, 2H).

Compound 3: Boronic acid 2 (2.5 g, 10 mmol) and tribromide 1 (2.5 g, 4.5mmol) were suspended in a mixture of Toluene (12 mL), EtOH (7 mL), andH₂O (12 mL). The mixture was purged with N₂ and treated with Na₂CO₃ (2.5g, 24 mmol). After 10 min Pd(PPh₃)₄ (0.47 mg, 0.41 mmol) was added andthe mixture was heated at 75° C. for 15 h. The reaction mixture wascooled, transferred to a separatory funnel, diluted with H₂O (100 mL)and extracted with EtOAc. The organic layer was washed with brine, driedand concentrated to give a foam. The crude product was chromatographedthrough SiO₂ (EtOAc:Hexanes, 1:9) to give compound 3 and 3a. Yield 31.25 g, 41%. Yield 3a 1.44, 43%. ¹H NMR compound 3 (400 MHz, CD₂Cl₂, 25°C.) δ 7.40 (m, 1H), 7.55 (m, 1H), 7.68 (m, 5H), 7.88 (m, 8H), 8.21 (t,2H), 8.60 (d, 2H), 8.93 (d, 2H); ¹H NMR compound 3a (400 MHz, CD₂Cl₂,25° C.) δ 7.69 (m, 6H), 7.87 (m, 3H), 7.97 (m, 6H), 8.21 (m, 3H), 8.89(m, 3H), 9.13 (m, 3H).

Compound 4: To a flame dried 3-neck round bottom flask fitted with acondenser, a nitrogen inlet, and a rubber septum was added compound 3(700 mg, 1.04 mmol), pinacolato diborane (395 mg, 1.55 mmol), dry KOAc(153 mg, 1.55 mmol), and the cyclohexyl phosphine ligand S-Phos (32.0mg, 0.078 mmol). The flask was placed then protected from the atmosphereand was charged with anhydrous THF (10 mL) and the solution was degassedby purging N₂ through the stirred solution. After 15 min, the reactionmixture was charged with Pd(OAc)₂ (5.8 mg, 0.026 mmol) and the mixturewas heated at reflux for 12 h. After this time had passed, the reactionmixture was cooled to RT, diluted with EtOAc (25 mL) and filteredthrough celite. The filter cake was washed with EtOAc and the filtratewas concentrated to dryness. The residue was chromatographed throughSiO₂ with a mixture of EtOAc:Hexanes as eluent. ¹H NMR (400 MHz, CD₂Cl₂,25° C.) δ 1.35 (s, 12H), 7.51 (m, 1H), 7.68 (m, 4H), 7.90 (m, 9H), 8.14(s, 1H), 8.22 (m, 2H), 8.89 (m, 2H), 9.13 (d, 2H).

Compound 5: A biphasic mixture of toluene (10 mL)/H₂O (5.0 mL)/EtOH (5.0mL) containing Na₂CO₃ (1.10 g) was purged with nitrogen. To thissolution was added the borate compound 4 (0.440 g, 0.608 mmol),3,5-dibromopyridine (58.0 mg, 0.243 mmol) followed by Pd(PPh₃)₄ (25.0mg, 0.0219 mmol). The reaction was placed under an inert atmosphere ofnitrogen and heated at a gentle reflux for 16 h. The mixture was cooledto RT, transferred to a separatory funnel, extracted with EtOAc (3×30mL), and dried over Na₂SO₄. The crude material was chromatographedthrough SiO₂ and eluted with 1% MeOH/CH₂Cl₂ to afford the product as awhite foam. Yield 210 mg, 68%. ¹H NMR (400 MHz, CD₂Cl₂, 25° C.) δ 7.50(m), 7.66 (m), 7.84 (m), 7.97 (m), 8.04 (t), 8.20 (m), 8.25 (m) 8.87(m), 8.94 (m), 9.12 (m).

Example 2 Preparation of 6-CF3 Reference Compound (6)

A 6-CF3 reference compound (6) was prepared according to the generalprocedure shown in Scheme 2.

A biphasic mixture of toluene (50 mL)/H₂O (50.0 mL)/Dioxane containingNa₂CO₃ (2.9 g) was purged with nitrogen. To this solution was added the3,5-bis(trifluoromethyl)phenylboronicacid (4.26 g, 16.5 mmol), andtribromide 1 (3.0 g, 5.5 mmol) followed by Pd(OAc)₂ (2.0 mol % w.r.t toeach Br, 74 mgs, 0.33 mmol), dicyclohexylphosphine-2′,6′-dimethoxybiphenyl (2.5 equs w.r.t Pd(OAc)₂ (0.338 g). The reaction was placedunder an inert atmosphere of nitrogen and heated at a gentle reflux for16 h. The mixture was cooled to RT, transferred to a separatory funnel,extracted with EtOAc (3×30 mL), and dried over Na₂SO₄. The crudematerial was chromatographed through SiO₂ and eluted first with Hexaneto remove non-polar impurities and then with ethyl acetate:hexane=2:8 toobtain the product as a white foam. Yield 5.13 g. ¹H NMR (400 MHz,CD₂Cl₂, 25° C.) δ 7.70 (m), 7.9 (m), 7.96 (m), 8.00 (m), 8.04 (m), 8.18(m).

Example 3 Preparation of 3-CF3 Reference Compound (7)

A 6-CF3 ETL compound (5) was prepared according to the general procedureshown in Scheme 3.

A biphasic mixture of toluene (10 mL)/H₂O (10.0 mL)/Dioxane (50.0 mL)containing Na₂CO₃ (0.63 g) was purged with nitrogen. To this solutionwas added the 2-(trifluoromethyl)pyridine-5-boronicacid (0.7 g, 0.35mmol), and tribromide 1 (0.65 g, 0.2 mmol) followed by Pd(OAc)₂ (2.0 mol% w.r.t to each Br, 6.7 mg), dicyclohexylphosphine-2′,6′-dimethoxybiphenyl (2.5 equs w.r.t Pd(OAc)₂ (33 mg). The reaction was placed underan inert atmosphere of nitrogen and heated at a gentle reflux for 16 h.The mixture was cooled to RT, transferred to a separatory funnel,saturated sodium bicarbonate wash, extracted with EtOAc (3×30 mL), anddried over MgSO₄. The crude material was chromatographed through SiO₂and eluted first with Hexane to remove non-polar impurities and thenwith ethyl acetate:hexane=2:8 to obtain the product as a white foam.Yield 0.45 g. ¹H NMR (400 MHz, CD₂Cl₂, 25° C.) δ 7.75 (m), 7.82 (m), 7.9(m), 8.10 (m), 8.20 (m), 9.08 (m).

Tribornylated triphenyl benzene (8): A biphasic mixture of THF (20mL)/Dioxane (5.0 mL)/Dioxane containing Na₂CO₃ (2.9 g) was purged withnitrogen. To this solution was added the pinacolate diborane (4.89 g,19.2 mmol), and tribromide 1 (3.0 g, 5.5 mmol), potassium acetate (1.62g, 16.5 mmol) followed by Pd(OAc)₂ (2.0 mol % w.r.t to each Br, 74 mgs,0.33 mmol), dicyclohexylphosphine-2′,6′-dimethoxy biphenyl (2.5 equsw.r.t Pd(OAc)₂ (0.34 g). The reaction was placed under an inertatmosphere of nitrogen and heated at a gentle reflux for 12 h. Themixture was cooled to RT, transferred to a separatory funnel, extractedwith EtOAc (3×30 mL), and dried over Na₂SO₄. The crude material waschromatographed through SiO₂ and eluted with ethyl acetate:hexane=2:8 toobtain the product as a white foam. Yield 5.13 g. ¹H NMR (400 MHz,CD₂Cl₂, 25° C.) δ 1.4 (s), 7.5 (m), 7.8 (m), 7.85 (m), 8.2 (m).

Example 4 Preparation of 3-CF3 ETL Compound (9)

A 3-CF3 ETL compound (9) was prepared according to the general procedureshown in Scheme 4.

A biphasic mixture of toluene (10 mL)/H₂O (10.0 mL)/Dioxane (50.0 mL)containing Na₂CO₃ (0.388 g) was purged with nitrogen. To this solutionwas added the tribornylated triphenyl benzene (0.5 g, 0.2 mmol) and 2bromo-4-trifluoromethyl pyridine (0.491 g, 3 equs), followed by Pd(OAc)₂(2.0 mol % w.r.t to each Br, 10 mg), SPhos ligand (2.5 equs w.r.tPd(OAc)₂ (45 mg). The reaction was placed under an inert atmosphere ofnitrogen and heated at a gentle reflux for 12 h. The mixture was cooledto RT, transferred to a separatory funnel, saturated sodium bicarbonatewash, extracted with EtOAc (3×30 mL), and dried over MgSO₄. The crudematerial was chromatographed through SiO₂ and eluted first with ethylacetate:hexane=1:9 to obtain the product (3^(rd) product that got elutedfrom column chromatography) as a white foam. Yield 0.2 g. ¹H NMR (400MHz, CD₂Cl₂, 25° C.) δ 7.55 (m), 7.7 (t), 7.94 (m), 8.10 (s), 8.15 (s),8.2 (m), 8.5 (m), 8.98 (m).

Example 5 Preparation of 3-F Reference Compound (10)

A 3-F Reference compound (10 was prepared according to the generalprocedure shown in Scheme 5.

The boronic acid (6.5 g, 41.4 mmol) and tribromide 1 (5.0 g, 9.21 mmol)were suspended in a mixture of Toluene (25 mL), EtOH (15 mL), and H₂O(25 mL). The mixture was purged with N₂ and treated with Na₂CO₃ (5.5 g,53 mmol). After 10 min Pd(PPh₃)₄ (956 mg, 0.828 mmol) was added and themixture was heated at 75° C. for 15 h. The reaction mixture was cooled,transferred to a separatory funnel, diluted with H₂O (100 mL) andextracted with EtOAc. The organic layer was washed with brine, dried andconcentrated to give a crude solid. The crude product waschromatographed through SiO₂ (EtOAc:Hexanes, 1:9) to give compound 3.Yield 1.25 g, 41%. ¹H NMR compound 1 (400 MHz, CD₂Cl₂, 25° C.) δ 7.40(m, 1H), 7.55 (m, 1H), 7.68 (m, 5H), 7.88 (m, 8H), 8.21 (t, 2H), 8.60(d, 2H), 8.93 (d, 2H).

Example 6 Refractive Index

Refractive index of compounds 5, 6, 7, and 9 were measured byellipsometry. Refractive index decreased as the fluorine contentincreased.

In the context of the present invention, alkyl is intended to includelinear, branched, or cyclic hydrocarbon structures and combinationsthereof, including lower alkyl and higher alkyl. Preferred alkyl groupsare those of C₂₀ or below. Lower alkyl refers to alkyl groups of from 1to 6 carbon atoms, preferably from 1 to 4 carbon atoms, and includesmethyl, ethyl, n-propyl, isopropyl, and n-, s- and t-butyl. Higher alkylrefers to alkyl groups having seven or more carbon atoms, preferably7-20 carbon atoms, and includes n-, s- and t-heptyl, octyl, and dodecyl.Cycloalkyl is a subset of alkyl and includes cyclic hydrocarbon groupsof from 3 to 8 carbon atoms. Examples of cycloalkyl groups includecyclopropyl, cyclobutyl, cyclopentyl, and norbornyl. Alkenyl and alkynylrefer to alkyl groups wherein two or more hydrogen atoms are replaced bya double or triple bond, respectively.

Aryl and heteroaryl mean a 5- or 6-membered aromatic or heteroaromaticring containing 0-3 heteroatoms selected from nitrogen, oxygen orsulfur; a bicyclic 9- or 10-membered aromatic or heteroaromatic ringsystem containing 0-3 heteroatoms selected from nitrogen, oxygen orsulfur; or a tricyclic 13- or 14-membered aromatic or heteroaromaticring system containing 0-3 heteroatoms selected from nitrogen, oxygen orsulfur. The aromatic 6- to 14-membered carbocyclic rings include, forexample, benzene, naphthalene, indane, tetralin, and fluorene; and the5- to 10-membered aromatic heterocyclic rings include, e.g., imidazole,pyridine, indole, thiophene, benzopyranone, thiazole, furan,benzimidazole, quinoline, isoquinoline, quinoxaline, pyrimidine,pyrazine, tetrazole and pyrazole.

Arylalkyl means an alkyl residue attached to an aryl ring. Examples arebenzyl and phenethyl. Heteroarylalkyl means an alkyl residue attached toa heteroaryl ring. Examples include pyridinylmethyl andpyrimidinylethyl. Alkylaryl means an aryl residue having one or morealkyl groups attached thereto. Examples are tolyl and mesityl.

Alkoxy or alkoxyl refers to groups of from 1 to 8 carbon atoms of astraight, branched, cyclic configuration and combinations thereofattached to the parent structure through an oxygen. Examples includemethoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, and cyclohexyloxy.Lower alkoxy refers to groups containing one to four carbons.

Acyl refers to groups of from 1 to 8 carbon atoms of a straight,branched, cyclic configuration, saturated, unsaturated and aromatic andcombinations thereof, attached to the parent structure through acarbonyl functionality. One or more carbons in the acyl residue may bereplaced by nitrogen, oxygen or sulfur as long as the point ofattachment to the parent remains at the carbonyl. Examples includeacetyl, benzoyl, propionyl, isobutyryl, t-butoxycarbonyl, andbenzyloxycarbonyl. Lower-acyl refers to groups containing one to fourcarbons.

Heterocycle means a cycloalkyl or aryl residue in which one or two ofthe carbon atoms is replaced by a heteroatom such as oxygen, nitrogen orsulfur. Examples of heterocycles that fall within the scope of theinvention include pyrrolidine, pyrazole, pyrrole, indole, quinoline,isoquinoline, tetrahydroisoquinoline, benzofuran, benzodioxan,benzodioxole (commonly referred to as methylenedioxyphenyl, whenoccurring as a substituent), tetrazole, morpholine, thiazole, pyridine,pyridazine, pyrimidine, thiophene, furan, oxazole, oxazoline, isoxazole,dioxane, and tetrahydrofuran.

Substituted refers to residues, including, but not limited to, alkyl,alkylaryl, aryl, arylalkyl, and heteroaryl, wherein up to three H atomsof the residue are replaced with lower alkyl, substituted alkyl,alkenyl, substituted alkenyl, aryl, substituted aryl, haloalkyl, alkoxy,carbonyl, carboxy, carboxalkoxy, carboxamido, acyloxy, amidino, nitro,halo, hydroxy, OCH(COOH)₂, cyano, primary amino, secondary amino,acylamino, alkylthio, sulfoxide, sulfone, phenyl, benzyl, phenoxy,benzyloxy, heteroaryl, or heteroaryloxy.

Haloalkyl refers to an alkyl residue, wherein one or more H atoms arereplaced by halogen atoms; the term haloalkyl includes perhaloalkyl.Fluoroalkyl refers to an alkyl residue, wherein one or more H atoms arereplaced by fluorine atoms; the term fluoroalkyl includesperfluoroalkyl. Examples of fluoroalkyl groups that fall within thescope of the invention include CH₂F, CHF₂, and CF₃.

Approximating language, as used herein throughout the specification, maybe applied to modify any quantitative representation that is not to belimited to the specific quantity specified and could permissibly varywithout resulting in a change in the basic function to which it isrelated. Accordingly, a value modified by a term or terms, such as“about”, is not to be limited to the precise value specified. In someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value.

Any numerical value ranges recited herein include all values from thelower value to the upper value in increments of one unit provided thatthere is a separation of at least 2 units between any lower value andcorresponding higher value. As an example, if it is stated that theamount of a component or a value of a process variable such as, forexample, temperature, pressure, rate, time and the like is, for example,from 1 to 90, preferred from 20 to 80, more preferred from 30 to 70, itis intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32etc. are expressly enumerated in this specification. For values whichare less than one, one unit is considered to be 0.0001, 0.001, 0.01 or0.1 as appropriate. These are only examples of what is specificallyintended and all possible combinations of numerical values between thelowest value and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. An optoelectronic device comprising a substrate an anode, a cathode,an electroluminescent layer; and an electron transporting layercomprising inorganic nanoparticles dispersed in an organic matrix.
 2. Anoptoelectronic device comprising according to claim 1, wherein theinorganic nanoparticles have a bimodal particle size distribution.
 3. Anoptoelectronic device according to claim 1, wherein the inorganicnanoparticles comprise a metal oxide, an alkali metal fluoride, analkali earth metal fluoride, or a combination thereof.
 4. Anoptoelectronic device according to claim 3, wherein the inorganicnanoparticles comprise a metal oxide.
 5. An optoelectronic deviceaccording to claim 4, wherein the inorganic nanoparticles comprisesilicon oxide, titanium oxide, zinc oxide, an alkali metal fluoride, analkali earth metal fluoride, or a combination thereof.
 6. Anoptoelectronic device according to claim 1, wherein the inorganicnanoparticles are disposed at or near a surface of the electrontransporting layer adjacent to the cathode.
 7. An optoelectronic deviceaccording to claim 1, wherein concentration of the inorganicnanoparticles in the electron transporting layer ranges from about 5% byweight to about 50% by weight.
 8. An optoelectronic device according toclaim 1, wherein concentration of the inorganic nanoparticles in theelectron transporting layer ranges from about 15% by weight to about 30%by weight.
 9. An optoelectronic device according to claim 1, whereinconcentration of the inorganic nanoparticles in the electrontransporting layer ranges from about 15% by weight to about 25% byweight.
 10. An optoelectronic device according to claim 1, whereinparticle size of the inorganic nanoparticles ranges from about 10 nm toabout 100 nm.
 11. An optoelectronic device according to claim 1, whereinthe electron transporting layer comprises pyridinyl functionality. 12.An optoelectronic device according to claim 1, wherein a refractiveindex of the inorganic nanoparticles is less than a refractive index ofthe organic matrix.
 13. An optoelectronic device according to claim 1,wherein the inorganic nanoparticles have a refractive index less than orequal to about 1.7.
 14. An optoelectronic device according to claim 1,wherein the inorganic nanoparticles have a refractive index less than orequal to about 1.5.
 15. An optoelectronic device according to claim 1,wherein the inorganic nanoparticles have a refractive index less than orequal to about 1.4.
 16. An optoelectronic device according to claim 2,wherein the inorganic nanoparticles having a bimodal particle sizedistribution comprise a first subpopulation of inorganic nanoparticleshaving a mean particle size ranging from about 10 to about 50 nm.
 17. Anoptoelectronic device according to claim 2, wherein the inorganicnanoparticles having a bimodal particle size distribution comprises asecond subpopulation of inorganic nanoparticles having a mean particlesize ranging from about 50 to about 300 nm.
 18. An optoelectronic deviceaccording to claim 2, additionally comprising at least one chargecarrier injecting or transporting layer comprising inorganicnanoparticles having a bimodal particle size distribution and dispersedin an organic matrix.
 19. An optoelectronic device according to claim 1,wherein the inorganic nanoparticles comprise any one or more of BeF₂,MgF₂, CaF₂, SrF₂, BaF₂ or combinations thereof.
 20. An optoelectronicdevice according to claim 19 wherein the organic matrix comprises anyone or more of poly(9,9-mono- or disubstituted fluorene),tris(8-hydroxyquinolato) aluminum (Alq3), 2,9dimethyl-4,7-diphenyl-1,1-phenanthroline, 4,7-diphenyl-1,1O-phenanthroline, 2-(4-biphenylyl)-5-(4-t butylphenyl)-1,3,4-oxadiazole,3-(4-biphenylyl)-4-phenyl-5 (4 t butylphenyl)-1,2,4-triazole,1,3,4-oxadiazole-containing polymers, 1,3,4-triazole-containingpolymers, quinoxaline-containing polymers and cyano-PPV.